OAKLAND -- Despite earlier promises, Bay Area transportation leaders are unlikely to hear a definitive "go" or "no go" for a Sept. 3 opening date of the new Bay Bridge during a briefing set for Wednesday afternoon, the fifth in a series of updates following the catastrophic snapping of steel anchor rods on the $6.4 billion span in March.

The bridge engineering and construction team last week started retrofitting the key seismic stabilizers where 32 out of 96 high-strength bolts became brittle and broke.

However, additional tests designed to show whether others among the 2,306 steel fasteners used on the bridge are susceptible to fracturing aren't finished yet, the repair schedule on the broken bolts is still tentative, and the Federal Highway Administration's review of the proposed repairs and testing protocols isn't complete.

The new span of the Bay Bridge nears completion in Oakland, Calif. on Wednesday, April 17, 2013. (Kristopher Skinner/Staff) (Kristopher Skinner/Staff file)

A delayed announcement doesn't mean the bridge won't open to traffic Sept. 3. It does mean that commuters and opening celebration planning organizations must wait before they can ink the date on their calendars.

"Right now, the opening is scheduled for Labor Day weekend," Bay Area Toll Authority spokesman Randy Rentschler said Tuesday. "But we need three pieces of information back (test results, repair schedule and highway administration review) to determine if Labor Day can be met or not. The date will move if it needs to move, but we also know for sure that the bridge we are driving on today is not safe."

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Caltrans, California Transportation Commission and the Bay Area Toll Authority -- the three agencies overseeing the construction -- chose Labor Day weekend because they need four days to connect the traffic lanes to the new span at Yerba Buena Island and Oakland. Traffic volume typically drops during long holiday weekends, and the Bay Bridge motorists use today will be closed to all traffic during the switch.

Called a "seismic opening," it is the date the agencies also considered the earliest the new span could safely open to traffic and move motorists off the 1936 cantilevered truss bridge, which engineers have determined is highly likely to collapse in the next big earthquake.

Metropolitan Transportation Commission Executive Director Steve Heminger said the decision will ultimately be up to Gov. Jerry Brown.

The opening date suspense is just one of many thorns stemming from embarrassing fractures in the large but relatively common steel bolts.

State legislators, local officials and the public are clamoring for answers about who is to blame and who will pay for what could be as much as a $10 million repair job on a bridge that hasn't even opened yet.

On the other side of the aisle, the rod manufacturer, Dyson Corp. of Ohio, recently spoke publicly for the first time when its president said the company delivered fasteners built precisely to Caltrans' standards.

Gerdau Long Steel North America, which produced in Minnesota the steel used to make the anchor rods, has also said it met all the specifications, according to a story in the American Metal Market or amm.com.

In the meantime, a retired Alameda metallurgist who submitted an unsolicited bolt analysis two months ago that proved highly accurate is raising more questions around why the steel broke.

Yun Chung agreed in a 17-page letter to Toll Bridge Program Manager Tony Anziano that hydrogen was the culprit, but he said the metallurgists failed to address the extraordinarily high odds that all 32 bolts snapped at the first thread in the bottoms of their casings -- he put the chances at 1 in 5 billion. The ends of the rods sat in water for five years -- a source of hydrogen -- before they were tightened.

Unless Caltrans determines precisely why fasteners in key seismic components broke, the state cannot assure the public that the other high-strength steel pieces on the bridge exposed to a marine environment will be safe, Chung wrote.

Led by Salim Brahimi, a Canadian metallurgist who leads an international standards committee on fasteners, the team hired by Caltrans blamed the broken rods on a well-known phenomenon in which hydrogen atoms infiltrate the spaces between the grains in high-strength steel components and leave them vulnerable to fracture. The stronger the steel and the higher the load, the more susceptible the fastener is to hydrogen embrittlement.

The team concluded that hydrogen likely was trapped inside the steel during the hot-dipped galvanizing process, and that triggered embrittlement when contractors tightened the nuts on the rods.

Insufficient data exists to reach that conclusion, Chung wrote.

He offered to conduct an independent laboratory evaluation at a metallurgical material testing laboratory in Hayward at no cost to the state, then deliver his findings within three weeks. As of Tuesday, he had not received a response.

if you go
The Bay Area Toll Authority will hold a special meeting to hear an update on the status of the new Bay Bridge:
When: 1 p.m. Wednesday
Where: Joseph P. Bort MetroCenter, Lawrence D. Dahms Auditorium, 101 8th St., first floor, Oakland
Online: Listen to a live audio feed at www.mtc.ca.gov/meetings/schedule/index.htm.